1. Field of the Invention
The present invention generally relates to telecommunications and, more particularly, to circuit-based switching convergence with packet-based-switching involving retention and sharing of an existing Signaling Point Code.
2. Background Description
Communications infrastructure throughout the world has undergone constant evolution. Much of the world""s infrastructure in the public switching domain is comprised of several different technologies. Public switched telephone networks (PSTN) are heavily entrenched with circuit-based-switches and one technology of preference to support PSTN operations is common channel signaling system No. 7 known also as SS7. SS7 is a global standard for telecommunications defined by the International Telecommunications Union (ITU) Telecommunications Standardization Sector (ITU-T).
The standard defines the protocols and procedures used by network elements in the PSTN to exchange information over a digital signaling network to enable establishment, routing, and control of calls. The ITU definition of SS7 allows for national variants such as European Telecommunications Standards Institute (ETSI) standards that are used in Europe and, for North America, the Bell Communications Research and American National Standards Institute (ANSI) versions are used. SS7 calls are of various natures including wireless (cellular), wireline, data, and a plethora of telephone and data customer features such as credit card validation, voicemail access, paging, banking access, voice conferencing, data connectivity, Internet access, etc.
SS7 networks and protocols are typically used for basic call setup, management, and release, local number portability, toll free and toll wireline services. It also supports enhanced call features such as call forwarding, calling party name/number display, three way calling, wireless services such as personal communications services (PCS), cellular roaming, and mobile subscriber identification.
SS7 messages are exchanged between network elements over 56 or 64 kilobit per second bi-directional channels called signaling links. The three kinds of network elements in a SS7 network include a Service Switching Point (SSP), a Signal Transfer Point (STP), and a Service Control Point (SCP).
SSPs are switches that originate, terminate and release circuits to manage calls. SSPs can query an associated SCP to determine routing information on a given call. SCPs contain centralized databases.
Network traffic between signaling points can be routed by an STP packet switch. An STP routes incoming messages to an outgoing signaling link based on routing information contained in an SS7 message. To properly address and transport a signaling message, signaling points are uniquely identified by a Signaling Point Code (SPC). SPCs are contained in the routing label of the signaling message. An SPC is a 24-bit address that is partitioned in three fields: network identifier, network cluster and the network cluster member. The value in the network identifier field directly identifies the network to which a point code belongs.
A cluster is defined as a group of SPs that directly home on a mated STP pair. There can be a maximum of 255 SPs per cluster. This limit can be easily exhausted. Therefore, introduction of a new SP with a new SPC can be very problematic. According to ANSI standard T1.111.4, all SS7 messages received by network provider interconnecting STP must have an MTP L3 Network Indicator field encoded to National Networks (meaning message is formatted for national networks).
Only one primary SPC can be associated with an MTP L3 Network. The Multiple MTP Internal Networks capability of this invention allows to have up to 32 MTP internal networks, but more could be established, each associated with one primary SPC and some secondary SPCs. The SPC in each of 32 networks is used to create it""s own linkset and routeset data. All information defined per each network is independent of each other and may represent specific configuration. For Shared Point Code mapping, a logical mapping mechanism is implemented to associate one network to another so that routing is or is not permitted from one network to another. In the past, migrating from one switch to another required extensive use of physical links and substantial database configuration changes.
For redundancy needs, SCPs and STPs are usually deployed in mated pairs. Links between signaling points are also typically provisioned in pairs. An SSP typically has links to two separate STPs. SS7 links are of different logical functions. These links are known as A-links, B-links, C-links, D-links, E-links, and F-links each having a particular function. For example, A-links connect a signaling end point (e.g. STP or SSP) to an STP. An F-link typically connects two signaling end points (i.e., SSPs and SCP) and not usually used in networks with STPs, however F-links can be employed to provide testing capabilities.
PSTN circuit-based-switches commonly employ time-division-multiplexing (TDM) techniques to facilitate call connections throughout the network and employ SS7 to facilitate the signaling. TDM is a circuit-oriented transmission mechanism and reaches capacity constraints and throughput limitations quickly relative to packet-based transmission mechanisms. Historically, TDM has been a dominant technology and has broad deployment penetrations worldwide. Substantial financial and technological investment currently exists in TDM switches.
The advancement of technologies has propelled packet-based switching transmission systems to levels of service that make it possible to aggregate communications for voice and data together in a packet switch. In general, packet-based switching networks have greater overall bandwidth potential compared to circuit-switched networks. Further, packet-based switching is finding strong acceptance in such services as the Internet, banking, video services, general business commerce and the like.
The advent of soft-switches, those which typically utilizes Internet Protocol (IP) and/or Automatic Transfer Mode (ATM) technology to unify data and voice switching at very high bandwidth levels provides new telecommunication and data capabilities and thus provides a very attractive alternative to the more ubiquitous, circuit-based-switches. Soft-switches typically employ digital signal processors (DSPS), high-powered microprocessors, or even custom silicon to process the packet message traffic for both voice and data.
Soft-switches are becoming reasonable and desirable choices for PSTNs throughout the world and even for private networks. The overall costs for soft-switches are typically lower than those of comparable circuit-based switches. Further, greater development potential exists for software-driven applications to be combined or offered as options in soft-switching architectures as compared to their traditional circuit-based-switch counterparts. Soft-switches, as the name implies, rely extensively on embedded and layered software instead of traditional hardware-based solutions to create logical associations, easily maintainable and extendible features, and to provide unique applications and solutions in general. PSTN operating companies, as well as private corporations, have begun to invest heavily in soft-switch technologies to achieve these advantages over circuit-based switches.
Major obstacles to the conversion of switching network infrastructures exist, including the investment in circuit-based and the technical difficulties involving the actual physical conversion of a circuit-based switch to packet-based switch, while it is in operation and processing subscriber calls, and without significant disruption in services. Telecommunications service disruption is extremely undesirable to customers, even for relatively short periods of time. Additionally, adding new switches in a network, for capacity or technology reasons, can cause substantial support and database configuration update burdens on operating companies. Adding new equipment to an existing network can be a logistical challenge and must be accomplished with minimal disruptions to the existing network and customer base. Finally, information changes, such as usually considered an undesirable risk addressing and routing in existing and operating networks since it may cause inadvertent disruptions.
In general, transparent operations and incremental additions to feature capabilities are desired expectations when expanding networks. The convergence of packet-based switching and circuit-based switching technologies requires new techniques to overcome the numerous obstacles in converting from the traditional circuit-based switches to the more flexible and cost effective soft-switches.
It is therefore an object of the invention to provide a method and apparatus for sharing signaling point codes between a circuit-based-switch (CBS) and a packet-based-switch (PBS) during and after the convergence of service from an existing circuit-based-switch to a new packet-based-switch.
It is another object of the invention to provide a method to migrate subscribers from a circuit-based-switch to a packet-based-switch transparently so subscribers will not be burdened with service disruptions.
It is yet another object of the invention to provide a means to transparently replace a circuit-based-switch with a packet-based switch so that minimal disruptions or administrative changes to the existing public switching network is required.
Further, it is yet another objective of the invention to provide a means to bi-directionally route traffic between a packet-based-switch and circuit-based-switch so that signaling point codes of a SS7 network are reused, shared, and retained.
Further, it is still another objective of the invention to permit subscribers to be moved gradually over a period of time from the circuit-based-switch to the packet-based-switch with minimal service disruption so that both the circuit-based-switch and the packet-based-switch co-exist simultaneously to provide seamless service to current subscribers on both switches and also to new subscribers on the packet-based-switch.
Furthermore, it is yet another objective of the invention to create a proxy STP within the packet-based-switch to permit transparent routing of traffic between the circuit-based-switch and the STP when the packet-based-switch is inserted between them.
According to the invention there is provided a method and system to permit migration of subscribers and services from an existing TDM circuit-based-switch, which is a part of a SS7 PSTN (or private) network and serving as an SSP, to a new packet-based-switch. This invention serves to facilitate convergence of TDM circuit-based-switches to packet-based technologies and also provides for the sharing, retention, and reuse of an assigned SS7 signaling point code (SPC) of the circuit-based-switch. The method and system provides substantially transparent migration so that minimal network modification is required and negligible impact on subscriber service occurs. This is accomplished by the innovative use of novel and new capabilities within a packet-based-switch, or soft-switch such as the Siemens SURPASS hiQ9200, to progressively assume the role of the circuit-based-switch and become a proxy for the circuit-based-switch. The packet-based-switch is installed and configured to co-exist simultaneously with an existing circuit-based-switch populated with subscribers so that an STP of a SS7 network routes traffic to destinations and subscribers associated with the circuit-based-switch, through the packet-based-switch.
To accomplish this, a soft-switch is installed and configured in stages to permit incremental assumption of bi-directional traffic routing between an existing circuit-based-switch and the STP. The goal ultimately is the gradual transfer of circuit-based-switch subscribers to the packet-based-switch and, when appropriate, removal of the circuit-based-switch with little disruption in service and minimal administration changes in existing network elements. This invention involves the co-existence of an established and functioning circuit-based-switch simultaneously with a newly installed packet-based-soft-switch and the migration from the xe2x80x9coldxe2x80x9d circuit-based-switch to the xe2x80x9cnewxe2x80x9d packet-based-switch. This invention permits co-existence of these two systems using a shared SPC. The xe2x80x9coldxe2x80x9d switch may or may not be retired at the discretion of the operating company.
The soft-switch is first connected to the circuit-based-switch via a SS7 F-link or A-link and is assigned a new SPC. The soft-switch employs a new and powerful concept of multiple internal networks to manage the routing of traffic that will be expanded on below. An internal network is a software arrangement that represents traffic and interfaces by origination sources and termination destinations and provides a simple means of aggregating traffic types, permitting easier administration, and subsequently simplifying routing decisions.
An F-link configuration is used if substantial test traffic will be introduced to validate the integrity of the configuration prior to actual live subscriber service, otherwise an A-link configuration can be implemented after testing occurs or can be implemented immediately if no testing will be involved. Both switches are configured to support this new link and to recognize the new SPC of the packet-based-switch to circuit-based-switch linkset.
The packet-based-switch is also configured to accept a new SS7 A-link between itself and an STP node of SS7 network. However, the SPC assigned to the packet-based-switch to support this new link is purposely made identical to the assigned SPC of the circuit-based-switch, which is important to the transparent migration and sharing of the SPC and a critical aspect of this invention. Since the packet-based-switch is to become an intermediary for the circuit-based-switch, routing means is established within the packet-based-switch so that traffic that flows from the STP and meant for subscribers resident on the circuit-based-switch is recognized and identified at the packet-based-switch and is routed directly to the circuit-based-switch for termination. Conversely, routing functions in the packet-based-switch is established so that traffic originating at the circuit-based-switch is routed either to subscribers within the packet-based-switch or is routed onward to the STP and the network depending on the subscriber dialing requests.
Several types of routing mechanisms exist and are employed in the art and are known to those skilled in the art, but this mechanism is enhanced with multiple internal networks to simplify convergence. Once these connections, assignments and routing means are established, the physical connections from the STP to the circuit-based-switch are re-routed to establish new connections comprising a link from the STP to the packet-based-switch and a connection from the packet-based-switch to the circuit-based-switch.
At this point, the packet-based-switch is acting as an STP proxy for the circuit-based-switch, i.e.; the circuit-based-switch that was previously interacting with the STP directly is now interacting with the packet-based-switch as if it were still the STP. Any ISUP trunks connected from the circuit-based-switch to the PSTN are also migrated to the packet-based-switch incrementally in a manner that will minimize risk during the convergence. Once this step is complete, all traffic is routed through and by the packet-based-switch.
This migration method requires no immediate administrative subscriber changes in the circuit-based-switch and requires no administrative changes to the STP. All traffic flows inbound and outbound transparently to the subscribers. Since all traffic now flows through the packet-based-switch, it is a matter of discretionary administrative action to move subscribers from the circuit-based-switch to the packet-based-switch and making necessary routing changes in the packet-based-switch to terminate traffic to any new subscribers on the packet-based-switch. This transfer of subscribers can occur at the convenience of the operating company or responsible entity, which greatly reduces risk to service and reliability. Additionally, no new routing or point codes must be introduced into the SS7 network itself (i.e., at the STP or other existing network nodes) in order to facilitate the transfer of service from the circuit-based-switch to the packet-based-switch. This greatly reduces risk of incorrect routing or disruption of service within the network overall.
It is possible for a soft-switch to migrate all traffic to a packet-based network and eventually eliminate the need for any SS7 type networks.
So to recap the invention as a system, this invention includes a system for use in a communication network for transparently sharing a signaling point code between a circuit-based-switch and a packet based switch comprising a circuit-based-switch with local subscribers, the circuit-based-switch having an assigned first signaling point code; a packet-based-switch having an assigned second signaling point code; the packet-based switch connected to a signaling transfer point; a SS7 signaling link between the circuit-based-switch and the packet-based switch; and a routing function to route traffic to the circuit-based-switch local subscribers from the packet-based switch so that the first signaling point code matches the second signaling point code, that is the signaling point code is reused.